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Spinal fusions are performed to treat degenerative diseases, deformities, and trauma. These problems generally cause or allow displacement or rotation of a vertebra relative to the adjacent vertebra. The objective of spinal implants is to facilitate realignment and/or fixation of spinal elements for fusion. Clinical studies have demonstrated that surgeries using spinal implants are more effective in providing structure and rigidity to the spine, than surgeries in which implants are not used. The majority of existing spinal implants use metal rods or plates to restrict the relative motion of the adjacent vertebra while fusing takes place. Once the two vertebrae are fused there is no longer a need for the rods or plates which may later cause complications. Bone dowels may be implanted for fusion without rods or plates and remain with the vertebra leaving no foreign material.
A bone fusion, using threaded cylindrical dowel implants, may be performed between two adjacent vertebrae to restore the space originally occupied by a disc. To increase the surface area of contact between the flat vertebral end plates and the cylindrical dowel or the absorbable fixation screw surface, it is necessary to machine partial cylindrical concave surfaces on the flat vertebral end plates to conform to the dowel.
In the prior art a distractor, consisting of a tube with two protruding tangs, was used for initial distracting, maintaining distraction, and acting as a guide during machining and implantation. These tangs may be referred to in the literature as xe2x80x9cextended outer sleevesxe2x80x9d. The tangs are hammered into the disc space to force and maintain distraction. A number of problems are associated with this method of distraction.
(1) The hammering or impacting may cause trauma to the vertebrae, the ligaments, the blood vessels, and the nerves.
(2) Once the tube is in place it cannot be removed until the dowel is implanted. This prevents the surgeon from inspecting the disc space, the thread depth, or the endplate condition.
(3) Since the tangs are tapered 61, any movement of the tube causes a component of the holding force to tend to dislodge the tube.
(4) The tangs do not hold the tube reliably and they allow trapezoidal deformation, especially with the cervical vertebrae, which are smaller than the lumbar vertebrae.
In other designs wedges, paddles, or plugs distract the vertebra prior to inserting the tangs, however the same tube instabilities and vision obstructions remain. A more stable and more versatile system will eliminate these deficiencies.
U.S. Pat. No. 6,080,155 has many similarities to the present patent, however the 155 patent discloses a tube with tangs, which are driven or hammered into the disc space. It does not provide for removing the tube and retaining distraction and it has no clearance undercuts to avoid the vertebral protrusions. These vertebral protrusions are not accurately portrayed in the 155 patent figures. Better representations are shown in FIGS. 5, 6, 12, and 13 of the present patent.
U.S. Pat. No. 5,899,908 discloses a tube with small teeth, which are driven or hammered into the vertebra. Experience has shown that these teeth will not retain the distraction while the tube is guiding the tools inside of the tube. These teeth also do not provide for removal of the tube for inspection while retaining distraction. In the 908 patent the figures do not accurately portray the vertebral protrusions. Better representations are shown in FIGS. 5, 6, 12, and 13 of the present patent.
The purpose of the present invention is to provide a device and a method to prepare the flat surfaces on the intervertebral end plates to receive a cylindrical implant. This device comprises a distractor, a flange, a series of guide tubes, attachment screws and tools. The distractor is positioned between the vertebral end plates and produces spreading or distraction of the vertebrae. This distraction will assure that the disc space height will be restored. The disc need not be removed before distraction.
The distractor will remove a portion of the disc, a reamer means will later remove the remaining portion of the disc that would interfere with the thread tap and dowel insertion. Once the vertebrae are spread, the flange is placed over the distractor shaft and on to the distractor-centering disc. This disc will insure that the flange is concentric with the distractor. When the flange is in place, attachments screws are placed through the holes in the flange tabs and into the adjacent vertebrae to maintain rigid vertebral spacing while the tooling and implant are in use. The tube assures that the tools will be centered on and parallel to the vertebral end plates and remain fixed during the procedure. This in turn can facilitate removal of an appropriate amount of bone or cartilage material from each adjacent vertebra. The implant can then be inserted through the flange. A length stop is used to set the depths of each tool. After the machining is completed the implant can be guided through the tube and be contained in place with a holding means, preferably a screw thread. These machining and dowel insertion operations are well known to those skilled in the art.